<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Calculator</title>
</head>
<body>
<form method="post" action="/calc">
    <p>Expr: </p><textarea name="expr"></textarea>
    <p>Env: </p><textarea name="env"></textarea>
    <input type="submit" value="Calculate">
</form>
<p>Result: {{.}}</p>
</body>
</html>